Comparison of DNA Extraction Methods for the Quantification of Listeria monocytogenes in Dairy Products by Real-Time Quantitative PCR

Listeria monocytogenes is a common foodborne pathogen affecting public health. Thus, detecting L. monocytogenes, even at low levels, in food matrices is essential. However, the current culture methods used for its detection and quantification are time consuming and difficult owing to background flora and interference by food matrices. DNA-based assays depend on DNA extraction and purification techniques. No optimal DNA extraction kit has been developed for analyzing L. monocytogenes in dairy products by real-time quantitative PCR (RT-qPCR). Therefore, in this study, we aimed to determine the efficiency of three DNA extraction kits for detecting L. monocytogenes in dairy products by RT-qPCR. We tested the efficiency of three commercial kits for DNA extraction from L. monocytogenes artificially inoculated in milk and dairy products. For the PrepSEQ rapid spin sample preparation kit and Exgene Cell SV mini, the limit of detection of was 100, 100, and 101 CFU/mL L. monocytogenes in milk, processed cheese, and infant formula, respectively, whereas that of the QIAamp DNA mini kit was 101, 103, and 102 CFU/mL, respectively. In addition, the Exgene Cell SV mini was better than the PrepSEQ rapid spin sample preparation kit for obtaining a standard curve for RT-qPCR of L. monocytogenes DNA in milk and dairy products, with a high correlation coefficient and amplification efficiency. The results of this study may be valuable for diagnostic laboratories and for developing an effective extraction method for processing food samples, such as dairy products, to subsequently detect and quantify L. monocytogenes by RT-qPCR.